Analysis of substorm disturbances in the night time auroral zone

Based on magnetic and ionospheric observations, and on such of optical emission in a meridional chain of stations near 90 degrees E extending from L = 4 to L = 12, the high-latitude ionosphere was investigated during quiet and moderately disturbed day; In substorm the intensity and hardness of precipitating fluxes in the Harang discontinuity was found increased. In evening and near-midnight hours substorms are preceded by the start of an equatorward displacement of the E-region sporadic ionization zone. After that, the zone expands abruptly poleward, with a concurrent increase in its electron density. A discrete precipitation band lies inside the diffuse precipitation zone of low-energy electron fluxes, whose boundary can be determined both from the type of reflections on ionograms and from the background emission level, The maximum of the westward auroral electrojet lies not within the region of maximum conductivity but somewhat farther to the north. (C) 1997 COSPAR. Published by Elsevier Science Ltd.